1. Field of the Invention
The present invention relates generally to tunable fiber lasers.
This invention is made with government support under contract numbers MDA-972-94-1-0003 and MDA-972-98-1-0002, awarded by DARPA. The government may have certain rights in this invention.
2. Description of the Prior Art
Tunable lasers have applications in a wide variety of fields, including optical communications and spectroscopy. For trace gas monitoring, compact tunable (20-30 GHz), wavelength modulatable sources with output powers on the order of approximately 100 xcexcW and linewidths better than 100 MHz are in great demand for wavelength modulation spectroscopy. The availability of high performance erbium-doped fiber amplifiers and pumped lasers allows for tunable fiber lasers. Modulation and switching of optical signals are basic functions in an optical communication system. Through modulation, the information to be communicated is expressed in one or more parameters of a light signal, such as the amplitude, the polarization, the phase or frequency of the field, or of the magnitude or spatial distribution of the power and/or intensity. Through switching, the light signal may be routed through a network of optical nodes and connections.
Precisely wavelength-switchable narrow linewidth laser sources are of great interest for many photonic applications, such as for tuning xe2x80x9con and offxe2x80x9d narrow absorption lines in spectroscopic measurements, including the monitoring of resonantly absorbing species in DIAL (differential absorption LIDAR)-type applications. Wavelength-switchable narrow linewidth laser sources are also critically needed for several applications in WDM-based (wavelength division multiplexed) fiber optic communication systems. Key requirements for such multi-wavelength switchable sources for WDM/DWDM systems are: (1) an accurate match with the wavelength channels on the WDM/DWDM ITU grid, (2) an arbitrary set of such channels, (3) a capability for switching reliably to any channel between such a pre-selected arbitrary set of channels, (4) low crosstalk, and (5) microsecond (or faster) switching speeds.
Past multi-wavelength switchable sources have in general been limited to schemes that are either difficult to scale to a large number of wavelengths, or have relatively slow (millisecond) switching speeds. Laser arrangements such as those found in U.S. Pat. No. 5,504,771 also require the use of stable external xe2x80x9cwavelength lockersxe2x80x9d to prevent wavelength drift from the FFPs PZT tuning assembly. Multi-frequency lasers based on integrated-optic arrays of DBR and DFB lasers, or SOA (semiconductor optical amplifiers arrays integrated with AWGs (arrayed waveguide gratings) seem to satisfy most of the above requirements. However, these are relatively difficult and expensive to manufacture, particularly in small volumes or for custom applications that may require a combination of numerous arbitrarily-spaced channels on the WDM/DWDM ITU grid.
Therefore, there is still a need for a rapidly switchable multi-wavelength source that is relatively easy to manufacture for any customized set of arbitrary channels on the ITU grid.
It is therefore an object of the present invention to provide a rapidly switchable multi-wavelength source that is relatively easy to manufacture for any customized set of arbitrary channels.
It is a further object to provide precise wavelength switching and selectivity capable of achieving specifications needed for DWDM applications.
It is yet another object to provide continuously wavelength-tunable fiber lasers and rapidly and precisely wavelength-switchable fiber lasers.
It is yet another object to provide continuous wave output as well as pulsed laser source designs.
It is yet another object to provide for single-wavelength and multi-wavelength switchable and tunable emission.
It is yet another object to prevent wavelength drift from the FFPs PZT tuning assembly by providing stable wavelength intra-cavity filters through the use of fixed-wavelength fiber Bragg gratings.
It is yet another object to provide wavelength-modulatable and simultaneously rapidly wavelength-switchable narrow linewidth all-fiber laser design for ultrasensitive detection of single or multiple trace gas species.
It is yet another object to provide fine electronic tuning over a coarsely selected wavelength range.
It is yet another object to provide narrow linewidth outputs, superior power outputs, and lower RIN (relative intensity noise) than elaborate short cavity lasers.